Late period calculator

Later than most people think. A period is only meaningfully late relative to your own pattern: FIGO, the international body that defines normal menstrual cycles, counts anything from 24 to 38 days as a normal cycle length, and up to 7–9 days of variation from one cycle to the next as normal too. So if your cycles run 27 to 33 days, a day-32 start isn't late at all — it's Tuesday. That's why this calculator asks for your longest recent cycle and measures against it, not just your average. A period isn't genuinely late for you until it's past the longest cycle your body has recently produced.

Now. From the first day of a missed period onward, a home urine test is reliable — the FDA puts properly-used tests at up to 99% accuracy from the day your period was due, and every additional day late makes a real pregnancy even harder to miss, because hCG roughly doubles every two to three days in early pregnancy. Use first-morning urine if you can (it's the most concentrated), follow the box instructions exactly, and read the result in the time window stated. Testing before a missed period is where false negatives live; testing any day after it is the reliable zone.

A lot — because a period is the end result of ovulation weeks earlier, anything that delays or suppresses ovulation delays the period. Common culprits: significant stress, an acute illness or fever, travel and sleep disruption, rapid weight change or under-eating, heavy exercise, PCOS, thyroid problems, elevated prolactin, perimenopause, breastfeeding, and medications — including starting or stopping hormonal birth control and taking emergency contraception this cycle. One late cycle with a negative test is usually a one-off late ovulation. A repeating pattern of long or skipped cycles is what deserves a clinician's workup, because causes like PCOS and thyroid disease are diagnosable and treatable.

First, give it a week and test again. If you ovulated later than you think, implantation may have happened too recently for the first test to catch — a repeat test a week later with first-morning urine settles it for almost everyone. If the repeat is negative and your period still hasn't arrived, pregnancy becomes an unlikely explanation and the non-pregnancy causes become the likely ones: stress, weight or exercise changes, PCOS, thyroid, perimenopause, medications. Keep a note of dates as they happen. And there's a hard stop: if you reach 90 days with no period, see a clinician even with a stack of negative tests.

Three clear triggers. First, the ACOG threshold: no period for 3 months (90 days) when your cycles used to come regularly — that's secondary amenorrhea and warrants an evaluation regardless of test results. Second, a pattern change: cycles that repeatedly land outside the 24–38-day normal bounds, or that suddenly become much more erratic than your baseline for several cycles running. Third — and this one is urgent, not an appointment: if you're late, a pregnancy test is positive, and you develop severe one-sided lower-belly pain, shoulder-tip pain, dizziness, fainting, or heavy bleeding, go to emergency care now. Those are warning signs of an ectopic pregnancy, which cannot wait.

Yes. This calculator runs entirely in your browser: the dates and answers you enter are computed on your own device and are never sent to a server, stored, or shared — close the tab and they're gone. In a post-Dobbs world we treat cycle and pregnancy data as sensitive by default, which is exactly why this tool has no accounts, no tracking of your inputs, and nothing to subpoena. It's general educational information based on ACOG and FIGO guidance; it isn't medical advice or a diagnosis.